Stability-Oriented Dynamics and Control of Complex Rigid-Flexible Mechanical Systems Using the Example of a Bucket-Wheel Excavator

The focus of this thesis is the modeling and control of the boom of the Bucket-Wheel excavator, which represents a specific type of complex machine systems used in mining technology. Hereby the Bucket-Wheel boom is modeled as the three-dimensional flexible beam using the Euler-Bernoulli beam theory. Retaining higher-order terms in the nonlinear strain-displacement relationship, higher-order coupling effects between the overall motion and flexible deformations are considered in the modeling. Furthermore, the nonlinear modeling of the three-dimensional elastic boom is also considered with the additional elasticity of hoisting cables. More complex motions, especially the guided motion in combination with digging resistance forces, are mentioned and discussed. So far, the elasticity of the boom along with the interaction between the cutting head and the face material is taken into account. The effects of higher-order couplings between flexible deformations, hoisting cables, and digging resistance forces on dynamical responses of the Bucket-Wheel boom are illustrated by intensive simulation studies. Dynamic phenomena resulting from higher-order geometrical and dynamical couplings undergoing the guided motion and digging resistance forces are therefore analyzed in detail. The destabilizing effects leading to large deformations (may be critical) of the system due to the above mentioned couplings are shown in simulation results. Thus, the developed model as well as the related dynamic system representation gives a good base for the advanced study of the stability of the system in combination with the digging resistance forces.
For control analysis and design purposes, the nonlinear dynamical system of the Bucket-Wheel boom is approximated by the extended linear system with nonlinearities modeled by a suitable fictitious model. Based on this extended linear system, a high-gain PI-Observer is applied to estimate all states of the system and to reconstruct the time behavior of the nonlinearities. From this point of view, a high-gain PI-Observer-based state feedback control is realized in combination with disturbance rejection control approaches. Three disturbance rejection control approaches including the static disturbance rejection control approach, Davison approach, and
the extended approach of Davison are discussed for compensating nonlinearities. Simulation examples are included to illustrate the efficient suppression of vibrations as well as the stabilization of the system during the digging process of the Bucket-Wheel Excavator. The results show that the static disturbance rejection control approach cannot stabilize the system, while Davison approach and the extended
approach of Davison can stabilize successfully the system with the suitable dynamic feedback terms. Consequently, application of these approaches can improve operating ranges of the Bucket-Wheel excavator. Therefore, an exploitation productivity of the Bucket-Wheel excavators can be increased.

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